Electric clutch actuator with spring-loaded thrust piece

ABSTRACT

An electric clutch actuator having a housing, an electric motor, a gear mechanism and a spindle which is coupled to the electric motor via the gear mechanism, wherein the spindle has an output end which acts on a relief piston which is displaceably mounted on a guide piston which is mounted so as to be displaceable in the housing, wherein the relief piston is urged elastically away from the guide piston towards the spindle.

BACKGROUND

The invention relates to an electric clutch actuator having a housing, an electric motor, a gear mechanism and a spindle which is coupled to the electric motor via the gear mechanism.

The clutch actuator serves particularly to actuate a clutch in the drive train of a lorry. For this purpose, the spindle is coupled to a disengagement lever of the clutch such that the desired disengagement force can be applied via the necessary disengagement stroke.

The disengagement force can lie in the order of magnitude of 6200 N, and the stroke of the spindle for disengagement can be in the order of magnitude of 80 mm. During disengagement of the clutch, this stroke must be overcome in 180 milliseconds.

In spite of these high requirements on the performance of the clutch actuator, the latter has to be very smooth-running since it is required that, in the event of a defect, the spindle can be pressed back by the clutch spring into the engaged position. An appropriate return speed is approximately 5 mm per second.

In order to obtain the desired axial stroke of the spindle, the latter engages in a spindle nut which can be set in rotation by the electric motor via the gear mechanism. However, the connection between the spindle nut and the spindle is (particularly if the spindle nut is a recirculating ball nut) comparatively susceptible to wear if vibrations act on the spindle and/or the spindle nut over a long time period.

BRIEF SUMMARY

The object of the invention thus consists in preventing excessive wear of the spindle and of the spindle nut.

To achieve this object, there is provision according to the invention that the spindle has an output end which acts on a relief piston which is displaceably mounted on a guide piston which is mounted so as to be displaceable in the housing, wherein the relief piston is urged elastically away from the guide piston towards the spindle. The guide piston ensures that the spindle is guided precisely relative to the spindle nut, with the result that no or, at the most, minimum radial loads can act. The relief piston can lift from the guide piston when the spindle moves back into a starting position upon engagement of the clutch. In the state in which the relief piston is lifted from the guide piston, vibrations and jolts which are exerted on the guide piston by the vehicle and the clutch are not transmitted to the spindle. At the same time, all of the components continue to be situated in a defined position since the relief piston is urged elastically relative to the guide piston.

Use is preferably made of a relief spring in order to elastically urge the guide piston and the relief piston relative to one another. This spring can in particular be a compression spring by which the desired axial preloading force can be generated.

The relief spring can be arranged to a large part within a spring receptacle which is formed within the relief piston. This results in a short axial installation space.

The relief spring preferably extends around an outer surface of the relief piston. A compression spring having a large diameter can thus be used.

A customary preloading force for the relief spring lies in the order of magnitude of 10 N to 50 N. On the one hand, this force is high enough for all the components to be urged to a sufficiently strong degree with respect to one another and for vibrations relative to one another to be prevented. On the other hand, this force is low enough in order to prevent a situation in which forces acting on the guide piston are transmitted to the relief piston and thus to the spindle.

To decouple the spindle in the starting position from the guide piston, it is sufficient if the stroke of the relief piston relative to the guide piston lies in the order of magnitude of 1 mm to 4 mm, and preferably in the order of magnitude of 2 mm.

The relief piston is preferably arranged in a receptacle in the guide piston, said receptacle being open at the end facing the spindle, wherein a securing ring is arranged at the axial end of the receptacle such that the relief piston is held captively in the receptacle. The securing ring makes it possible to pre-assemble the relief piston on the guide piston together with the relief spring, thus simplifying the final assembly.

According to an alternative embodiment, it is also possible for the relief piston to be plugged into a receptacle in the guide piston and latched therein. The mounting of a separate securing ring can be dispensed with as a result.

A groove, in which a sliding element is arranged, can be provided in the outer circumferential surface of the relief piston and/or of the guide piston. This sliding element allows the friction of the guide piston in the receptacle of the guide piston or the friction of the relief piston in the guide piston to be reduced.

The sliding element can be a slotted ring which can be mounted in the groove with little effort. The ring can consist in particular of PTFE.

According to a preferred embodiment, a ring magnet whose magnetic field can be detected by a position sensor is arranged on the guide piston. In this way, the position of the guide piston can be detected upon actuation of the clutch.

The ring magnet can be pressed against the guide piston by a compression spring which is supported between the guide piston and the housing. It is thus not required for the ring magnet to be fixed separately on the guide piston.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described below on the basis of an embodiment which is illustrated in appended drawings. In these drawings:

FIG. 1 shows a longitudinal section through a clutch actuator;

FIG. 2 shows the detail II of FIG. 1 on an enlarged scale;

FIG. 3 shows a section along the plane III-III of FIG. 2;

FIG. 4 shows a section along the plane IV-IV of FIG. 3;

FIG. 5 shows the detail V of FIG. 1 on an enlarged scale;

FIG. 6 shows the region VI of FIG. 1 in a section plane which differs from the section plane of FIG. 1;

FIG. 7 shows a section along the plane VII-VII of FIG. 6;

FIG. 8 shows the plug shown in FIG. 6 in a perspective view;

FIG. 9 shows, in an enlarged view, an alternative contacting of the printed circuit board shown in FIG. 6;

FIG. 10 shows a view similar to that of FIG. 3, wherein a cover and an intermediate gear wheel have been removed;

FIG. 11 shows a detail of the gear mechanism in a perspective view;

FIG. 12 shows a detail of the gear mechanism in a further perspective view;

FIG. 13 shows the cover used for the housing in a perspective view;

FIG. 14 shows the sliding guide for the spindle in a perspective view;

FIG. 15 shows a section through the sliding guide of FIG. 14; and

FIG. 16 shows the movement path of the spindle during the actuation of the disengagement lever.

DETAILED DESCRIPTION

An electric clutch actuator can be seen in FIG. 1 that serves to actuate a disengagement lever of a friction clutch which is arranged in the drive train of a motor vehicle, in particular of a lorry.

The clutch actuator 1 has an electric motor 10 which is coupled to a spindle nut 40 via a gear mechanism 20. The spindle nut 40 is fixed in the axial direction and is seated on a spindle 60 which can be adjusted in the axial direction by rotation of the spindle nut 40. The spindle 60 interacts with a pressure plunger 80 which in turn interacts with a disengagement lever of the clutch (not shown here).

The spindle nut 40 is a recirculating ball nut here, resulting in low friction between the spindle and the spindle nut.

The supporting constituent part of the clutch actuator 1 is a housing 3 which (apart from a cover 5) is configured in one piece. A stator receptacle 7 and a spindle guide 9 are provided in particular in the housing 3.

Since the housing is configured in one piece, in particular being cast, the wall thickness between the stator receptacle 7 and the spindle guide 9 can be configured to be comparatively thin. This results overall in very small dimensions, in particular a small distance between the centre axis of the electric motor 10 and the centre axis of the spindle 60.

An aluminium alloy is preferably used as the material for the housing 3. The production process preferably used is a die-casting process.

The electric motor 10 is a brushless electric motor which has a stator 12 and a rotor 14. The stator 12 contains a plurality of stator windings which are adapted to the respective requirements. The rotor 14 has a plurality of permanent magnets. The latter are arranged on a motor shaft 16 which is mounted in the housing 3 by means of rolling bearings 17, 18.

The housing 3 has a mounting opening 4 on the bottom 6 of the stator receptacle 7. The mounting opening 4 serves to guide the rotor 14 when it is inserted into the stator 12. For this purpose, a suitable tool can be inserted into the mounting opening 4. The mounting opening 4 is in particular a locating bore.

The gear mechanism 20 has a pinion 22 which is connected to the motor shaft 16 for conjoint rotation, an intermediate gear wheel 24 and driving teeth 26 which are assigned to the recirculating ball nut 40.

The driving teeth 26 are here part of a driving gear wheel which is connected to the recirculating ball nut 40 for conjoint rotation. According to an alternative embodiment, the driving teeth 26 are formed in one piece on the outer circumferential surface of the recirculating ball nut 40.

The intermediate gear wheel 24 is a two-stage gear wheel which has an input toothing 28, in which the pinion 22 engages, and an output toothing 30, which interacts with the driving teeth 26 of the recirculating ball nut 40. As can be seen particularly in FIG. 4, the input toothing 28 and the output toothing 30 are provided in one piece on the intermediate gear wheel 24.

The diameter of the output toothing 30 is greater than the diameter of the input toothing 28. There results overall a step-down from the motor shaft 16 to the recirculating ball nut 40 that lies in the order of magnitude of 4.2:1 to 4.4:1.

The intermediate gear wheel 24 itself is mounted on a bearing pin 32 which is fixedly mounted on a base plate 34. In the exemplary embodiment shown, the bearing pin 32 is pressed into the base plate 34.

The intermediate gear wheel 24 is mounted on the bearing pin 32 by means of two needle bearings 36. A shaft sealing ring 38 is respectively provided on both sides of the needle bearings 36.

The base plate 34 serves to receive all the components of the gear mechanism 20 and to mount them relative to one another with low tolerance. This particularly concerns the rolling bearing 18 by which the motor shaft 16 is mounted, the bearing pin 32 by which the intermediate gear wheel 24 is mounted, and a rolling bearing 42 by which the recirculating ball nut 40 is mounted on the base plate 34.

The base plate 34 is a solid metal plate which is inserted into a shoulder provided in the housing. Said base plate can be screwed in the housing 3. In addition, it is braced against the housing 3 by the cover 5 (see in particular FIG. 2).

The rolling bearing 42 is a four-point bearing since it allows a slight deviation of the orientation of the centre axis of the recirculating ball nut 40 from its ideal orientation. The recirculating ball nut 40 can thus be optimally oriented if the spindle 60 is deflected in the radial direction on account of acting transverse loads.

In the exemplary embodiment shown, the four-point bearing 42 has an inner ring 43 which is pressed onto the outer surface of the recirculating ball nut 40, and an outer ring 44 which is held fixedly with respect to the housing.

According to an embodiment variant (not shown), the raceway for the rolling bearing balls of the four-point bearing 42 can also be ground directly into the outer surface of the recirculating ball nut 40.

The spindle 60 has an output end 62 which is arranged on the right-hand side in FIG. 1, said output end interacting with a guide piston 68 which is displaceably received in the housing 3 and which in turn interacts with the pressure plunger 80. For this purpose, the guide piston 68 is provided with a concave receptacle 70 in which the end of the pressure plunger 80 facing away from the disengagement lever of the clutch engages.

The guide piston is mounted so as to be displaceable in the spindle guide 9 in the housing 3, with the result that the spindle 60 is also precisely guided in an axially oriented manner when a radial force component is exerted by the pressure plunger 80.

The guide piston 68 has a cylindrical extension 66 which forms a piston receptacle 67 in which a relief piston 64 is received. On its side facing the spindle, the relief piston 64 has a concave receptacle in which the output end 62 of the spindle 60 is received.

The relief piston 64 is displaceable in the piston receptacle 67 in the axial direction, a relief spring 74 being arranged between the relief piston 64 and the guide piston 68 and urging the relief piston 64 relative to the guide piston 68 out of the piston receptacle 67 in the axial direction towards the spindle 60.

The relief spring 74 is here arranged between a bottom of the receptacle which is formed within the extension 66 and a shoulder on the relief piston 64. As a departure from the embodiment shown in which the relief spring 74 externally surrounds a portion of the relief piston 64, the relief spring 74 can also be arranged in a recess of the relief piston 64 that is open towards the guide piston 68.

In the exemplary embodiment shown, the extension 66 has a securing ring 76 on its open side facing away from the pressure plunger 80, with the result that the relief piston 64 is held captively within the piston receptacle 67 of the extension 66.

The relief piston 64 has a groove 78, in which a sliding element 79 is arranged, on its outer circumferential surface. The sliding element 79 is here a slotted ring made of plastic, in particular of PTFE. The sliding element 79 ensures that the relief piston 64 is displaceable in the axial direction within the extension 66 with low friction.

In order also to mount the guide piston 68 in a low-friction manner, two sliding elements 79 are provided which are likewise configured as slotted plastic rings which preferably consist of PTFE. In the same way as for the relief piston 64, the sliding elements 79 are arranged in a respective groove 78 in the outer circumferential surface. They therefore guide the guide piston 68 within the spindle guide 9.

In the spindle guide 9 there is arranged a compression spring 82 which is supported between the recirculating ball nut 40 and the guide piston 68, thus urging them away from one another. On the side of the recirculating ball nut 40, the compression spring 82 is supported here on an abutment plate 84.

On the side of the guide piston 68, the compression spring 82 is supported on an abutment ring 86 which consists of plastic. The latter bears in turn against a ring magnet 88 which, just like the abutment ring 86, is arranged on the extension 66. On account of the action of the compression spring 82, the ring magnet 88 is positioned and held on the guide piston 68 and moves together therewith.

Furthermore, the outer ring 44 of the four-point bearing 42 is axially preloaded by means of a disc spring 89, with the result that the recirculating ball nut 40 is always held in a defined, stabilized position. The disc spring is supported by its outer circumference on the outer ring 44 of the four-point bearing 42 and by its inner circumference on the abutment plate 84.

The ring magnet 88 interacts with a position sensor 90 which is arranged on the outer side of the extension 66 of the guide piston 68. The position sensor 90 can be a Hall sensor or GMR sensor.

As an alternative to the ring magnet 88, use can also be made of a segmented magnet with corresponding rotational securement on the guide piston 68.

As an alternative to a measuring system with a Hall or GMR sensor, an inductive measuring system is also possible. In this case, a target would be used instead of the ring magnet.

A further sensor is provided for detecting the rotation of the motor shaft 16. This sensor is arranged in the region of the mounting opening 4 (see in particular FIGS. 6 to 8).

On the motor shaft 16 there is arranged a magnet 92 whose magnetic field can be detected by a sensor 94. The sensor 94 is in particular a GMR sensor. Alternatively, it is in principle also possible to use a Hall sensor.

The sensor 94 is arranged on a carrier which is here formed by a printed circuit board 96 which is fixedly connected to a holder 98 made of plastic. In the exemplary embodiment shown, the printed circuit board 96 is screwed to the holder.

The printed circuit board 96 is arranged, together with the holder 98, in a pocket 99 which extends in the radial direction with respect to the centre axis of the motor shaft 16 and intersects the mounting opening 4.

For precise functioning of the sensor 94, it is important that it is oriented precisely relative to the motor shaft 16. For this purpose, the mounting opening 4 is used in the embodiment shown.

A plug 100 which interacts with a holding opening 102 in the holder 98 of the printed circuit board 96 is inserted in the mounting opening 4.

The plug 100 has a body part 104 whose outer dimensions correspond to the inside diameter of the mounting opening 4. Furthermore, the body part 104 is provided with a sealing ring 106 which seals within the mounting opening 4. In addition, the plug 100 is provided with a latching extension 108 which is slotted multiple times such that it can be compressed in the radial direction.

The latching extension 108 engages in the holding opening 102 such that the holder 98 and thus, via the printed circuit board 96, also the sensor 94 are positioned relative to the mounting opening 4. Since the mounting opening 4 is configured as a locating bore which is concentric to the centre axis of the motor shaft 16, the sensor 94 is thus also centred onto the centre axis of the motor shaft 16.

As can be seen in FIG. 7, the printed circuit board 96 has a plurality of connection contacts 110 at its end facing away from the sensor 94. Here, either a cable 112 can be connected by which the printed circuit board 96 is connected to a main board, or the connection contacts 110 can be configured as press-in contacts (see FIG. 9) which are inserted into corresponding contact openings of a main board 114 when the main board 114 is mounted.

FIGS. 10 to 13 show details of the gear mechanism 20.

According to the variant shown here, the base plate 34 is fastened in the housing 3 using a number of screws 114.

A particular feature of the gear mechanism 20 is that there is provided a grease guide which ensures that grease present on the toothing cannot migrate into other regions.

The grease guide consists, firstly, of a bushing 120 which surrounds the output toothing 30 of the intermediate gear wheel 24 (with the exception of the region which allows the engagement in the driving teeth 26 of the recirculating ball nut 40).

The grease guide has, furthermore, a collar 122 which is configured in one piece with the cover 5 and extends from the cover towards the base plate 34.

Here, the collar 122 surrounds the pinion 22, the intermediate gear wheel 24 and the driving teeth 26 of the recirculating ball nut 40.

It can be seen in FIGS. 14 and 15 how the spindle 60 is held in a rotationally fixed manner such that it does not corotate when the recirculating ball nut 40 is driven.

At the end opposite the output end 62 of the spindle 60, the latter is provided with a carriage 130 which is mounted on the spindle 60 in a rotationally fixed manner. For this purpose, the spindle 60 can be provided at this end with a square geometry, a hexagonal geometry or another suitable geometry.

The carriage 130 is displaceably received in a sliding guide 132, wherein the sliding guide is provided on the inner side with two longitudinal grooves 134 in which suitable lugs 135 of the carriage 130 engage. The carriage 130 is thus displaceable in the axial direction within the sliding guide 132. In addition, it is displaceable in the radial direction within certain limits, since the dimensions of the lugs 135 are slightly smaller than the dimensions of the longitudinal grooves 134.

The sliding guide 132 is a component made of plastic which is latched into the cover 5 of the housing 3. Latching tabs 136 can be used for this purpose.

FIG. 16 shows the geometric conditions for the adjustment of the pressure plunger 80. Its front end is adjustable between the two positions designated by the reference sign 80 ₁ and the reference sign 80 ₂. The position 80 ₂ corresponds to a disengaged clutch in the new state. In the engaged position, the front end of the pressure plunger 80 (with new clutch) is situated about 25 mm left of the position 80 ₂.

The stroke of the pressure plunger 80 is in the order of magnitude of 80 mm, with the result that a stroke in the order of magnitude of 55 mm is available for readjusting the disengagement lever in the case of wear.

From the radius of the disengagement lever, which is about 160 mm, and the maximum adjustment travel of the pressure plunger of 80 mm, there results a pivoting movement of the pressure plunger 80 by about 4 degrees between the two maximum positions 80 ₁, 80 ₂, since the end of the pressure plunger 80 that interacts with the disengagement lever also executes a radial movement between the engaged and the disengaged position.

In order to keep the loads on the guide piston 68 as low as possible, the centre axis M of the spindle 60 is oriented in such a way that it is situated approximately centrally between the orientation of the pressure plunger 80 in the two extreme positions 80 ₁ and 80 ₂.

The possible displacement travel of the guide piston 68 in the spindle guide 9 is considerably greater than the stroke for actuating the clutch. This is due to the fact that the clutch actuator 1 is used for readjusting the disengagement lever in the case of wear. In the new state of the clutch, the guide piston 68 is situated close to the right end of the spindle guide 9 and is adjusted to the right from there by the actuating stroke. Towards the end of the service life of the friction linings of the clutch, the guide piston 68 is situated at the left end of the spindle guide 9 and is adjusted to the right from there by the actuating stroke.

When the clutch actuator 1 engages the clutch, that is to say releases the disengagement lever, by the spindle 60 being driven to the left (with respect to FIG. 1) by the recirculating ball nut 40, the spindle 60 always executes a stroke which is greater by 1 to 2 mm than the stroke of the pressure plunger 80. Upon engagement of the clutch, it is possible, via the position sensor 90 and the ring magnet 88, to recognize when the guide piston 68 under the action of the clutch spring is not further adjusted within the spindle guide 9.

However, after the guide piston 68 has come to a standstill, the spindle 60 is further adjusted. Consequently, the relief piston 64 under the action of the relief spring 74 lifts from the bottom of the piston receptacle 67 within the extension 66. For this purpose, the electric motor 10 is further operated until such time as the relief piston 64 is separated from the guide piston 68 by the functionally desired distance (about 2 mm). The signal desired for this purpose pertaining to the number of revolutions of the electric motor 10 is provided by the sensor 94. The functionally required distance of about 2 mm between the relief piston 64 and the guide piston 68 ensures that the spindle 60 and hence the recirculating ball nut 40 are separated from the pressure plunger 80 and consequently no vibrations and load change stresses can be transmitted to the recirculating ball nut 40.

If the clutch is intended to be disengaged, first the play between the relief piston 64 and the guide piston 68 is removed. The spindle 60 then presses the guide piston 68 to the right with respect to FIG. 1, with the result that the clutch is disengaged. 

The invention claimed is:
 1. An electric clutch actuator comprising: a housing, an electric motor, a gear mechanism and a spindle which is coupled to the electric motor via the gear mechanism, wherein the spindle has an output end which acts on a relief piston which is displaceably mounted on a guide piston which is mounted so as to be displaceable in the housing, wherein the relief piston is urged elastically away from the guide piston towards the spindle.
 2. The electric clutch actuator according to claim 1, wherein a relief spring is arranged between the relief piston and the guide piston.
 3. The electric clutch actuator according to claim 2, wherein the relief spring is arranged to a large part within a spring receptacle which is formed within the relief piston.
 4. The electric clutch actuator according to claim 2, wherein the relief spring extends around an outer surface of the relief piston.
 5. The electric clutch actuator according to claim 2, wherein the relief spring provides a preloading force in the order of magnitude of 10 N to 50 N.
 6. The electric clutch actuator according to claim 1, wherein the stroke of the relief piston relative to the guide piston lies in the order of magnitude of 1 mm to 4 mm.
 7. The electric clutch actuator according to claim 1, wherein the relief piston is arranged in a piston receptacle on the guide piston, said receptacle being open at the end facing the spindle, wherein a securing ring is arranged at the axial end of the piston receptacle such that the relief piston is held captively in the piston receptacle.
 8. The electric coupling actuator according to claim 1, wherein the relief piston is plugged into a piston receptacle in the guide piston and latched therein.
 9. The electric clutch actuator according to claim 1, wherein a groove is provided in the outer circumferential surface of the relief piston and/or of the guide piston, wherein a sliding element is arranged in the groove.
 10. The electric clutch actuator according to claim 9, wherein the sliding element is a slotted ring made of plastic, in particular of PTFE.
 11. The electric clutch actuator according to claim 1, wherein a ring magnet is arranged on the guide piston.
 12. The electric clutch actuator according to claim 11, wherein the ring magnet is pressed against the guide piston by a compression spring which is supported between the guide piston and the housing.
 13. The electric clutch actuator according to claim 11, wherein a position sensor is provided in the housing, with which sensor the position of the guide piston is detected.
 14. The electric clutch actuator according to claim 1, the output end of the spindle acts directly on the relief piston. 